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Stable oscillation of AlGaInP diode laser with phase-conjugate feedback
Minoru Obara,Akira Shiratori,Ryuji Aida 慶熙大學校 레이저 工學硏究所 1996 레이저공학 Vol.7 No.-
During the last decade, much attention has been paid to a diode laser with phase-conjugate feedback(PCF). Because the phase-conjugate feedback beam traces exactly back to the extremely small active region of the diode laser, selfaligning of the external phase conjugator and mechanical stability of the laser system can be easily achieved. By taking the unique advantage of PCF, several improvements of diode lasers such as spectral narrowing, beam shaping of LD arrays, and mode locking have ever been demonstrated.
Catalytic Control Requirement for the Closed-Cycle High-Repetition-Rate Operation of a TEA CO₂Laser
Minoru Obara,Hirokazu hokazono,Naoki Kobayashi 慶熙大學校 레이저 工學硏究所 1991 레이저공학 Vol.2 No.-
Using the newly developed 1 kHz, closed-cycle transversely excited atmospheric (TEA) CO₂ laser with the efficient CO₂ regenerator including the Pt/Al₂O₃ solid catalyst, we experimentally determined the minimum operational performance of CO₂ regenerator, which is required for the stable and long-life operation of the closed-cycle TEA CO₂ laser. The operational performance of the CO₂ regenerator was evaluated by the fractional conversion (η) from CO to CO₂, which is defined as the ratio of the differential CO₂ concentration increased by the CO₂ regenerator to the total CO concentration introduced into the CO₂ regenerator. The minimum fractional conversion (Πmin) of 0.07 was at least required to keep the laser output power at 95% of the initial laser output for the laser gas mixture of CO₂/N₂/He=15/15/70(%) and at input energy density and a clearing ratio of 150 J/l and 6.0, respectively. When operating the CO?? regenerator at Πof 0.10, no appreciable reduction of the initial laser output of 570W due to CO₂ decomposition was observed up to 1.8 ×10?? shots (5 hours). At this time, the gas analysis showed that the CO and O₂ concentration in the laser gas mixture was maintained about at 0.17% and 0.055%, respectively.
Tsunenori Arai,Minoru Obara,Miya yoshikawa,Makoto Kikuchi,Satoko Kawauchi,Hiroko Matsuyama 慶熙大學校 레이저 工學硏究所 1996 레이저공학 Vol.7 No.-
We developed novel monitoring of corneal surface hydration during photorefractive keratectomy (PRK) in order to improve undercorrection of the central part of cornea (Central Island), which might be attributed to excessive hydration. We employed pulsed photothermal radiometry(PPTR), noncontact and noninvasive method to measure the absorption coefficient, to monitor corneal surface hydration. We performed two model experiments: gelatin gel experiments and porcine corneal in vitro experiments. In the case of the gelatin gel experiments, the absorption coefficient of the gelatin gel was changed by gelatin density. The e-folding decay time of transient infrared radiation waveform from the irradiated surface was prolonged with decreasing gelatin density. This measured e-folding decay time was good agreement with the result of theoretical calculations. Using porcine cornea, we observed the e-folding decay time extension during ArF excimer laser ablation of the porcine cornea. Our method may be available to improve the reproducibility in PRK.
Preparation of BaTiO₃ Thin Films using Pulsed KrF Laser Deposition and in situ Laser Annealing
Akihiko Machida,Atsushi Ito,Minoru Obara 慶熙大學校 레이저 工學硏究所 1996 레이저공학 Vol.7 No.-
Barium titanate (BaTiO³) thin films have been fabricated on MgO substrate using a hybrid process of pulsed KrF laser deposition (PLD) and in situ laser annealing. By utilizing in situ excimer laser annealing, epitaxial films of 1 ㎛ thickness were successfully fabricated and its refractive index was close to that of the bulk crystal. Substrate temperature to fabricate epitaxial films was relatively low at 650℃, and smooth surface films were achieved with this method.
Hiroshi Kumagai,Koichi Toyoda,Mizunori Ezaki,Minoru Obara,Kyoichi Adachi 慶熙大學校 레이저 工學硏究所 1996 레이저공학 Vol.7 No.-
Epitaxial rare-earth (Re: Nd and Yb) and transition-metal (Tm:Cr) doped yttrium aluminum garnet (Re??:Y??Al??O??) films have been grown on various substrates by pulsed laser deposition for the purpose of fabricating diode-pumped waveguide microchip lasers. The films were characterized by Rutherford backscattering, x-ray diffraction, and photoluminescence measurements. TheseNd:YAG films on (100) silicon substrate having a large lattice mismatch show oriented stoichiometric growth. On the other hand, the films of Nd, Yb and Cr doped YAG on garnet substrates show the epitaxial growth with the smooth surfaces. Their characterization of rare-earth doped YAG thin films on various substrates was comparable to that of the rare-earth doped YAG bulk laser crystals.